1. Field of the Invention
The present invention relates generally to the art of storage batteries and more particularly to thin, SLI (storage, lighting, ignition) batteries of the type which do not require bulky or heavy containers, covers, straps or conventional battery venting systems. Still more specifically, the present invention relates to a battery made by locating pasted plate grids on plastic sheeting, folding the sheeting, accordion style, electrically connecting certain of the plates and then sealing the sheeting to produce a flat, high voltage battery.
2. Description of the Prior Art
Traditional lead-acid batteries suffer from the characteristic ohmic resistance provided by the electrode grid, grid lug, electrode current strap and intercell connections. Moreover, traditional lead-acid batteries are bulky and require space consuming containers, covers, venting devices and the like. These components add considerably to the weight of battery, a problem with today's lightweight automobiles, the desire to continually improve fuel efficiency. Bipolar batteries have been suggested as an alternative because of the elimination of some of these components. Because bipolar batteries have a thin, lightweight construction, it has been suggested that such batteries may be used as replacements for many traditional SLI applications.
Generally, a bipolar battery is one having positive and negative active materials adhered to opposite sides of a conductive plate substrate. The function of the bipolar substrate is to allow current to pass from one electrode to the other through the substrate, thereby eliminating the need for grid lugs, current straps and intercell connections. Bipolar plates can be tightly stacked against each other, with suitable electrolyte present, thus occupying less space. Examples of such bipolar batteries are shown in Biddick, et al. U.S. Pat. No. 4,098,967 issued Jul. 4, 1978 and Eskra, et al. U.S. Pat. No. 4,900,643 issued Feb. 13, 1990.
Biddick, et al. suggests the use of conductive plastic substrates, while the Eskra, et al. patent describes a substrate of plastic conductive material having a metallic wire mesh disposed therein. In the latter patent, a single sheet of wire material is folded about the conductive plastic, tent style, and embedded in the plastic to provide structural and electrical advantages.
Another patent which discusses the use of folding for battery construction is U.S. Pat. No. 4,406,057 issued Sep. 27, 1983 to Oswald, et al. In this patent, an element stack is provided using relatively small electrode plates positioned in a spaced apart manner along a strip of separator material. The strip is folded, accordion style, and the stack is completed by inserting a second set of electrode plates of opposite polarity in the folds. The patentees suggest that the construction technique is amenable to automation and that the resulting cell stack may be handled as a unit thereby facilitating battery assembly.
While the latter patent does disclose a flat stack battery of bipolar nature, the patent still suffers from the drawbacks encountered by trying to pass electrons through a substrate material rather than from conductive grid to conductive grid. Moreover, the placement of electrode plates in the proper position in an accordion fold, where alignment is particularly important, creates manufacturing difficulties.
Pearson, in U.S. Pat. No. 4,530,153 issued Jul. 23, 1985 for "Manufacturing Recombination Electric Storage Cells" describes a cell pack of alternating positive and negative electrodes interleaved with separator material. The active material is damp when the layers are inserted into a plastic bag, and the cell pack is cured to a dry state while in the bag. In an illustrated embodiment each electrode is folded once about an electrode of opposite charge, and individual cells are connected by spot welding together adjacent take-off lugs, each of which is located on an upper edge of a folded electrode. A final rigid housing contains the multi-cell packs. The battery does not include individual cell pouches or any continuous strip of material to facilitate rapid fabrication of the battery.
There continues to exist, therefore, a need for lightweight batteries of a monopolar design which do not require bulky, expensive and heavy containers, current straps, etc. It would also be highly desirable to provide a fast battery construction technique which could be adapted to a wide variety of battery sizes and shapes.
It has also been proposed in the bipolar battery art to use "duck-bill" type venting systems for the gasses generated during battery formation. Such a system is described in U.S. Pat. No. 5,004,655 by Symanski, issued Apr. 2, 1991 for "Thin Bipolar Lead-Acid Battery With Individual Cell Vent". In this application, a frame is provided for the electrode and separator materials, the frame including vent passageways. The frame is sandwiched between sheeting of insulating plastic. A duck-bill type vent system is provided at the peripheral edge of the overlapping and sealed plastic to allow gases of formation to escape. It would be desirable to have such a venting system in a monopolar, thin optimized lead-acid battery.